a) Field of the Invention
The present invention relates to a semiconductor laser apparatus used as a laser source of an optical pickup apparatus which records/reproduces information on an optical recording medium. More specifically, it relates to a semiconductor laser apparatus which feedback-controls the amount of light from a semiconductor laser.
b) Description of the Related Art
The amount of laser beam light (determined by the intensity of the laser beam light) emitted from a semiconductor laser largely varies depending on temperature and a change in time. Therefore, it is a common practice to feedback-control the amount of light from the semiconductor laser for obtaining a constant amount of light from the semiconductor laser. For example, in a semiconductor laser described in Tokkai H4-349687, a step is formed on the surface of a semiconductor substrate wherein a semiconductor laser is placed at the lower surface of the step and an optical detector for monitoring is formed on the side wall of the step. As a result, the semiconductor laser and the optical detector for monitoring are placed opposite from each other while an optical detector for detecting signals is formed at a location other than the side wall of the step.
Nonetheless, in the above semiconductor laser apparatus of Tokkai H4-349687, the configuration is such that the semiconductor laser and the optical detector for monitoring are placed opposite from each other by using a step formed on the semiconductor substrate. Therefore, a drawback exists in that the optical detector for monitoring cannot be formed on a semiconductor substrate having a flat surface; in turn, it is difficult to form the optical detector for detecting signals and the optical detector for monitoring on the same surface. As a result, the two optical detectors are formed in separate processes such that costs for manufacturing the semiconductor laser apparatus are dramatically increased.
If a light receiving plane of the optical detector for monitoring is formed on a semiconductor having a flat surface, on the other hand, only a small part of a laser beam emitted from the semiconductor laser reaches the light receiving plane; as a result, precision in detection of light beams deteriorates.